Chapter 7 Notes_DS
Chapter 7: Cellular Respiration & Fermentation
I. Overview of ATP Generation
Three Processes to Generate ATP:
A. Aerobic Respiration
Efficient process requiring O2.
Most organisms can use this process at times.
Also referred to as cellular respiration; different from breathing but related in that both involve gas exchange (breathing is the physical intake of O2).
B. Anaerobic Respiration
Similar to aerobic, but does not use O2.
Mainly utilized by bacteria in O2-deficient environments.
C. Fermentation
Inefficient process used when other pathways can't be utilized or when quick ATP is needed.
Does not rely on O2.
II. Aerobic Respiration: A Redox Process
Basic Definition:
Most efficient form of cellular respiration for most organisms.
Catabolizes nutrients (typically glucose) to CO2 and H2O, storing energy in ATP.
Chemical Equation:
C6H12O6 + 6 O2 + 6 H2O → 6 CO2 + 12 H2O + Energy (36-38 ATP).
Key Points:
Redox Process: Glucose is oxidized to CO2 and O2 is reduced to H2O.
Complex series of reactions includes the combustion of glucose equivalent to burning but captures energy without excessive heat release.
III. Stages of Aerobic Respiration
Divided into Four Stages:
A. Glycolysis
Occurs in cytosol (in both prokaryotes and eukaryotes).
Process: Converts glucose into 2 pyruvate molecules; net yield is 2 ATP and 2 NADH.
2 Phases:
Energy Investment Phase:
Uses 2 ATP for phosphorylation, forming 2 G3P.
Energy Payoff Phase:
Converts G3P to pyruvate.
Produces 4 ATP (net 2) and 2 NADH.
Overall Reaction:
C6H12O6 + 2 ADP + 2 Pi + 2 NAD+ → 2 C3H3O3 + 2 ATP + 2 NADH + 4 H+ + 2 H2O.
B. Formation of Acetyl CoA
Pyruvate moves to mitochondria (eukaryotes) or stays in cytosol (prokaryotes).
Involves oxidative decarboxylation: removal of CO2, formation of NADH, and creation of acetyl-CoA.
Overall Reaction:
C3H3O3 + NAD+ + CoA → Acetyl-CoA + CO2 + NADH.
C. Citric Acid Cycle
Also known as TCA cycle or Krebs cycle, occurring in mitochondria.
Process:
Acetyl-CoA combines with oxaloacetate to form citrate.
Produces 3 NADH, 1 FADH2, and 1 ATP per cycle.
Overall Reaction:
Acetyl-CoA + 3 NAD+ + FAD + ADP + Pi → CoA + 2 CO2 + 3 NADH + FADH2 + ATP.
D. Oxidative Phosphorylation
Occurs in mitochondria; involves the electron transport chain (ETC) and chemiosmosis.
Electrons from NADH & FADH2 are transferred to the ETC, ultimately reducing O2 to form water.
Proton pumping creates a gradient, leading to ATP synthesis via ATP synthase.
Energy yield from NADH is ~3 ATP, and from FADH2 is ~2 ATP.
IV. Energy Yield of Aerobic Respiration
Theoretical Yield:
36-38 ATP from one glucose molecule.
Actual yield typically around 30 ATP due to energy used for non-ATP reactions (like pyruvate transport).
V. Non-Glucose Energy Sources
Other substrates can be oxidized for ATP, including proteins and lipids:
A. Proteins:
Broken into amino acids; can enter respiratory pathways after deamination.
B. Lipids:
Yield more energy than glucose; glycerol converts to G3P, while fatty acids undergo β-oxidation to form acetyl-CoA.
Example: oxidation of a 6-carbon fatty acid can yield up to 44 ATP.
VI. Regulation of Aerobic Respiration
ATP/ADP Balance:
Rapid ATP usage leads to an increase in ADP, promoting further aerobic respiration.
Key Enzyme:
Phosphofructokinase is subject to allosteric regulation by ATP (inhibitor) and AMP (activator).
VII. Anaerobic Respiration
Utilized by bacteria in O2-deficient environments.
Follows similar steps as aerobic but with different electron acceptors (like NO3-, SO4^2-, CO2).
Less efficient than aerobic respiration.
VIII. Fermentation
Occurs with no electron transport chain, yielding only 2 ATP from glycolysis.
Requires regeneration of NAD+, resulting in two types:
A. Alcohol Fermentation:
Converts pyruvate to ethanol and CO2 to regenerate NAD+.
Example: used by yeast in fermentation processes (alcohol, baking).
B. Lactic Acid Fermentation:
Converts pyruvate to lactate to regenerate NAD+.
Occurs in certain bacteria, fungi, and mammalian muscle cells under oxygen-limited conditions.